The auditory cortex exhibits a broad range of response modes spanning from phasic, single spike or binary responses to tonic, multi-spike, sustained random firing sequences per stimulus. The goal of this project is to determine the character of response variability of different types of auditory cortical neurons in the awaken squirrel monkey. This will allow us to assess the potential role and influence of variability on neuronal encoding, and its impact on behavioral performance and to compare the results to other response modalities. To achieve this, it is necessary to obtain simultaneous estimates of neural and behavioral performance in the awaken animal. Response variability will be assessed under three conditions, in the passive listening animal to serve as a baseline, in the animal actively involved in a behavioral sound discrimination task to assess attention effects, and in animals that are highly trained to assess the effects of learning on the expression of response variability. In conjunction with the other projects, these studies will contribute to establishing general rules, across sensory and motor systems, of the nature and role of response variability in the generation of behavior.